Generation of gigahertz-repetition-rate femtosecond vortex beams by an optical parametric oscillator

The generation of GHz-repetition-rate femtosecond vortex beams is reported for the first time, to the best of our knowledge. A self-developed GHz-repetition-rate Kerr-lens mode-locked Yb:CYA laser was used to pump an optical parametric oscillator (OPO). Hermite-Gaussian (HG) beams with tunable orders from the 1st to the 7th were generated in the OPO and subsequently converted into vortex beams of the corresponding orders outside the cavity. The generated vortex beams exhibit a repetition rate of 1.02 GHz, a wavelength tuning range spanning 1.47-1.66 μm, and a pulse duration ranging from ~100 fs to ~200 fs. This work provides a flexible and reliable approach for generating GHz-repetition-rate femtosecond vortex beams and offers a high-performance optical source for relevant applications.